Process of superficially saponifying a strip of cellulose ester

ABSTRACT

A foil, film or the like of a fatty acid ester of cellulose which contains more than 1.5 but less than 3 molecules of combined fatty acid per glucose residue is subjected to superficial saponification in a bath containing an alkaline substance and an organic solvent, and when the saponification has proceeded to the desired depth the foil or other article is treated in one or more baths which terminate the saponification, at least one of these after-treatment baths being one which contains no aqueous solution of monobasic or dibasic acid but which is capable of reducing aqueous swelling of partially esterified cellulose having 0.5 to 1.5 molecules of combined fatty acid per glucose residue.  Such an after-treatment bath may be a solution of a water-soluble sulphate, phosphate, sulphite, thiosulphate, carbonate, tartrate, citrate, acetate, lactate, fluoride or chloride.  It may be an aqueous solution of a tribasic acid or of glycerol, glucose or a sugar.  It may be a primary saturated alcohol having a straight chain of 4-11 carbon atoms, such as butanol-1.  An after-treatment bath containing toluene, benzene, tetrahydronaphthalene or a liquid ether may be used.  The treated films may be used for photographic purposes, e.g. the saponified layers may be impregnated with light-sensitive substances.  If desired, plasticizers originally present in the films may be removed from the saponified layers by solvent treatment, e.g. by treatment with aqueous or alcoholic-aqueous solutions of dispersing agents such as salts of sulpho-ricinoleic acid, sodium oleate, sodium p-octylbenzene sulphonate, dodecylamine hydrochloride and lauryl ethers of polyethylene oxide.  The substance for reducing aqueous swelling and the solvent for the plasticizer may be incorporated in a single treatment bath.  In an example, a cellulose acetate tape is passed in succession through a solution of caustic potash in aqueous methanol, through two baths of butanol-1, through an aqueous solution of phosphoric acid and through two baths of circulating water.

PROCESS OF 'SUPERFICIALLY SAPONIFYING A STRIP OF CELLULQSE Roelof JanHendrik Alink, Johannes Cornelis Antonius aSPe a i Will m Y B isSs f inmin el, Ein 'dhoven, Netherlands, assignors to Hartford Naonal Bank andTrust Company, Hartford, Conn, as .mlstee L, No Drawing. Originalapplication June 6, 195, Serial o: 230,245, new Patent No;2;704,-262;dated March 15, 1955. Divided and this application January '13, 1955,Serial No. 481,714 r Claims priority, application Netherlands June 6,1950 Claiuns. (Cl. 117-62) This invention relates to an improved methodof making cellulosic and more particularly to cellulosic films which areto be subsequently impregnated with ig se itive system containing'adi'afzoniumcompound, and is 'a division of our 'co-pen'ding application,,Ser. No; 230,- I-2 45,1fi1ed June 6, 19 1, new U Pat n No- 2,704,262.'Fat'tyacidesters of cellulose film's containing from 1.5 to 3.0radicals offatty acid per glucose unit were sa'ponified in order toregenerate a cellulosic outerlayer which'can be readily impregnated withaqueous solutions; Such had the undesirable feature that 'the outerlayer swelled in aqueous solution while the unsaponified portion of thefilm did not swell, resulting stresses in the filrn withfsubsequentpeeling of the outer -l yer.

United States Patent C) (I An o'bject'of the invention, therefore, is toprovide a v fethod to shrink the outer layer and to prevent its subeqent Peelin and further objects of my invention will appear asthe'speciiication progresses. i "According to the invention, thecellulose strip after euperficial saponification thereof is immersed inone or more aftentreatrnent baths. One of theafter-treatments containsananti-peeling agent which shrinksan'int'ermg diate partially 'saponifiedlayer such that upon subsequent immersion of the strip in an aqueoussolution, for instance when impregnating the strip with 'a water-solublelightsensitive system no stresses are created in the saponified layerwhich would cause it to peel from the underlying unsaponified portion ofthe strip.

The invention is particularly applicable to cellulose diesters which aresubject to peeling after saponification. For example a fatty ester ofcellulose containing more than 1.5 and less than 3.0 fatty acid radicalsper glucose residue after superficial saponification, i. e. by immersionof a strip of this material in a saponifying bath for a given period oftime to saponify at least one side of the strip to a desired depth, isimmersed in a bath containing an anti-peeling agent which is capable ofshrinking a layer intermediate the outer surface of the strip and theunsaponified portion of the strip which contains 0.5 to 1.5 fatty acidradicals per glucose residue.

Anti-peeling agents suitable for the aforesaid purposes are: primarysaturated alcohols having a main chain of from 4 to 11 carbon atoms,such as butanol-l; a mixture of about one part of butanol-l and aboutone part of either benzene or toluene; a mixture of about one part ofbutanol-l and about one part of tetrahydronaphthalene; a mixture ofabout one part of butanol-l and about one part of diethyl ether; asolution of about 1.5 n phosphoric acid and butanol-l.

Cellulosic films which initially contain ester plasticisers such astriphenylphosphate and tricresylphosphate, which upon the superficialsaponification of tha fatty acid cellulose ester are not saponifiedcompletely. Particularly the intermediate layer may hold or subsequentlyattract from the substratum by diffusion a comparatively large PatentedAug. 14,

2 amount of plasticiser resulting in deposition or turbidity ofparticles of plasticiser on the surface ofthe film, foil or the like.It'ha's now been'found that the plasticjser still present aftersapon'ific at'ion" in the totally sapz'mifi a layer and the intermediatelayer of the rott'fil'mw'r the like can be removed with the use ofsolvents. Such solvents are, for example, solutions of so-calleddispersion agents]? such as salt of a 'sulphated hy droxycarbdni c acidhaving at least 10 carbon atoms, for example, nium'or sodiunisalts ofricinolic acid 'esterified with s'ul} phu iC a id, in additionsodiumoleate, the sodium s'altof pfoctylbenzenesulphonic acid, cationegenou'sdispersion agents such as dodecylaminehydrochloride or compo nds derivedtherefrom and in addition nc'm-ion forming persion agentasuch aspolyethers, derived from methylene for ethylene oxide, which at the endof the chain,'ar e eisterified, for example, witha lauryl alcohol.Solutionsof fr e? 5 to by We h o these on-f m d ers qn agents in' waterare suited to free from plasticis'er saponified superficial layers offoils, films or the like made'of fatty acid cellulose esters. Anafter-treatment bath may contain both an antipeeling ag'ent forpartially esterified cellulose containing from 0.5 to 1.5 radicals offattyacid per glucose residue and a solvent for the plasticiser. It mustbe noted that'ja great number of non-ion-form'ing shrinkinga'gent's'also have a dissolvingefiect on plasticisers. l

Since the intermediate layer formed during saponificationdoes notjswellappreciably'in the solution of the dis- ,Pi r' iQi a e ere r obabil f hapon fie layer peeling from the non-saponified substratum; "Th'r 'e s eo fe t l er y 'es d o h choic between treating the foil, film or thelike upon saponificatio11" first with the use of the dispersionagentorlby treating it first 'the use of the anti-peeling agent. For th e"'sake" of p c y r t s agent nd t e s lven r th plasticiser maybe combinedin one after-'treatment'bath.

"The'invention will now described in connectionf'with thefollowingexamples:

Exam I A mechanically moved web 130 ,u. thick and made of celluloseacetate containing about 2.3 radicals of acetic acid per glucose unit issaponified at 24 C. for 45 seconds on two sides in a solution of l npotassium hydroxide in a mixture of 66 parts by volume of methanol and34 parts by volume of water, shrinking then taking place for a period of45 seconds in a mixture of 1 part by volume of butanol-l and 1 part byvolume of toluene. The web then passes during a period of 45 secondsthrough a stopper bath of 0.6 n acetic acid in butanol-l. Eventually theweb is washed in circulating water for 2.5 minutes and after sprayingwith water and skimming dried with the use of warm air of about to C.

The thickness of the regenerated cellulose layer is 10 n and that of theintermediate layer 4 ,u. The adhesion of the saponified layer to thenon-saponified substratum is excellent. The butanol-toluene mixture maybe replaced with equally satisfactory results by a mixture of butanol-lwith benzene or with tetrahydronaphthalene or with diethyl-ether.

Example II A web ,u. thick and made of cellulose acetate having anacetic acid content of 53.3% is passed mechanically at 23.5 C. at therate of 60 seconds per bath in succession through the following baths:

use being made with advantage of the difierence in specific gravitybetween butanol-l and water so that the film upon immersion in bath ([1)repels the alcohol.

The web is then sprayed with water for 30 seconds and after skimming at90 C. dried with a warm flow of air. The thickness of the regeneratedcellulose layer is a and that of the intermediate layer 3 The adhesionof the saponified layer to the substratum is excellent.

Examp le III Cellulose diacetate foil was superficially saponified for 1minute in a solution of l n-potassium hydroxide in a mixture of 2 partsby volume of methanol and 1 part by volume of water at 25 C. The web wasthen immediately inserted in a solution obtained by diluting 10 ccs. of89% phosphoric acid with 300 cos. of butanol-l (this solution is about1.5 .n). After immersion in this bath for 1 minute at 25 C. the foil wasrinsed in water for 30 minutes and then dried in air. The saponifiedlayer adheres most satisfactorily and the surface is smooth. It

is preferred that the concentration of phosphoric acid should not beexcessive since otherwise the surface of the saponified layer, which initself is readily adhesive, tends to become slightly shrivelled.

While the invention has been described with reference to specificexamples and applications thereof, other modifications will be readilyapparent to those skilled in the art without departing from the spiritand scope of the invention as defined in the appended claims.

What we claim is:

1. A process of superficially saponifying a strip of cellulose estercontaining between 1.5 and 3.0 radicals of fatty acid per glucoseresidue, which comprises the steps of immersing said strip in asaponifying bath containing at least 0.1 normal solution of an alkalihydroxide and an alcoholic solvent to effect rapid saponification ofsaid strip for a time sufficient to produce a partially saponified layerin said strip containing between 0.5 and 1.5 fatty acid radicals perglucose residue, and thereafter immersing said strip for at least 45seconds in butanol-l.

2. A process of superficially saponifying a strip of cellulose estercontaining between 1.5 and 3.0 radicals of fatty acid per glucoseresidue, which comprises the steps of immersing said strip in asaponifying bath containing at least 0.1 normal solution of an alkalihydroxide and I,

an alcoholic solvent to eflfect rapid saponification of said strip for atime suflicient to produce a partially saponified intermediate layer insaid strip containing between 0.5 and 1.5 fatty acid radicals perglucose residue, and thereafter immersing said strip for at leastseconds in a mixture of about one part of butano'l-l and about one partof a component having the formula CnH(2n-6), where n is one of theintegers 6 and 7.

3. A process of superficially saponifying a strip of cellulose estercontaining between 1.5 and 3.0 radicals of fatty acid per glucoseresidue, which comprises the steps of immersing said strip in asaponifying bath containing at least 0.1 normal solution of an alkalihydroxide and an alcoholic solvent to effect rapid saponification ofsaid strip for a time sufiicient to produce a partially saponifiedintermediate layer in said strip containing between 0.5 and 1.5 fattyacid radicals per glucose residue, and thereafter immersing said stripfor at least 45 seconds in a mixture of about one part of butanol-l andabout one part of tetrahydronaphthalene.

4. A process of superficially saponifying a strip of cellulose estercontaining between 1.5 and 3.0 radicals :of fatty acid per glucoseresidue, which comprises the steps of immersing said strip in asaponifying bath containing at least 0.1 normal solution of an alkalihydroxide and an alcoholic solvent to effect rapid saponification ofsaid strip for a time sufiicient to produce a partially saponifiedintermediate layer in said strip containing between 0.5 and 1.5 fattyacid radicals per glucose residue, and thereafter immersing said stripfor atleast 45 seconds in a mix-v ture of about one part of butanol-land about one part of diethyl ether.

5. A process of superficially saponifying a strip of cellulose estercontaining between 1.5 and 3.0 radicals of fatty acid per glucoseresidue, which comprises the steps of immersing said strip in asaponifying bath containing at least 0.1 normal solution of an alkalihydroxide and an alcoholic solvent to efiect rapid saponification ofsaid strip for a time sufficient to produce a partially saponifiedintermediate layer in said strip containing between 0.5 and 1.5 fattyacid radicals per glucose residue, and thereafter immersing said stripfor at least seconds in a solution of about 1.5 n phosphoric acid inbutanol-l.

No references cited.

1. A PROCESS OF SUPERFICIALLY SAPONIFYING A STRIP OF CELLULOSE ESTERCONTAINING BETWEEN 1.5 AND 3.0 RADICALS OF FATTY ACID PER GLUCOSERESIDUE, WHICH COMPRISES THE STEPS OF IMERSING SAID STRIP IN ASAPONIFYING BATH CONTAINING AT LEAST 0.1 NORMAL SOLUTION OF AN ALKALIHYDROXIDE AND AN ALCOHOLIC SOLVENT TO EFFECT RAPID SAPONIFICATION OFSAID STRIP FOR A TIME SUFFICIENT TO PRODUCE A PARTIALLY SAPONIFED LAYERIN SAID STRIP CONTAINING BETWEEN 0.5 AND 1.5 FATTY ACID RADICALS PERGLUCOSE RESIDUE, AND THEREAFTER IMMERSING SAID STRIP FOR AT LEAST 45SECONDS IN BUTANOL-1.